Automatic pilot servo system



April 28,v 1959 P. A. NoxoN AUTOMATIC PILOT sERvo SYSTEM Original Filed May 29, 1944 Iknr wm vota( nited States Patent AUTOMATIC PILOT SERVO SYSTEM Paul A. Noxon, Tenatly, NJ., assignor to Bendix Aviation Corporation, Teterboro, NJ., a corporation of Delaware Original applications May 29, 1944, Serial No. 537,952, and October 24, 1949, Serial No. 122,792. Divided and this application January 12, 1951, Serial No. 205,750

, 17 Claims. (Cl. S18-489) The present invention relates to an automatic navigational control system adapted for use with dirigible craft and constitutes a division of Noxon and MacCallum application Serial No. 122,792, filed October 21, 1949, now Patent No. 2,772,059, which, in turn, is a division of Noxon, MacCallum and Murphy application Serial No. 537,952, filed May 29, 1944 now Patent No. 2,838,258.

Where both parent application Serial No. 537,952 and divisional application Serial No. 122,792 are directed to a novel all electric, three axes of control automatic pilot for mobile craft including automatic turn and other novel features therein pointed out and described in detail, the present application is directed to a single control channel ofthe above automatic pilot, such as 'the rudder channel,

for example, wherein a signal generator is actuated by a reference or position-maintaining means for operating a servo actuated control surface, a second signal generator being actuated in response to control surface positioning for developing a follow-up signal to modify surface positioning together with a trim signal generator by the use of which craft position may be changed in spite of the fact that the reference or position-maintaining means attempts to maintain a predetermined position, craft position' change being effected through the trim signal generator without disconnecting the reference or position-maintaining means from the control channel.

An object of the present invention, therefore, is to pro vide a novel control channel for use in automatically stabilizing an aircraft about any desired axis thereof, such stabilization being provided by the algebraic summation of reference and surface follow-up signals.

Another object is to provide a novel control channel for use in automatically stabilizing an aircraft about any one of its control axes, such channel being provided with a course or attitude change device between the reference maintaining means and the surface servo motor whereby course or attitude changes may be effected without disconnecting the reference maintaining means from the control channel.

A further object is to provide a novel control channel for use in automatically stabilizing an aircraft about any desired axis thereof wherein sensitivity control adjustment is provided to predetermine surface response to one or more control signals.

The above and other objects and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawing wherein one embodiment of the invention is illustrated. Itis to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not designed as a definition of the limits of the invention.

T he single ligure of the drawing is a diagrammatic illustration of the novel automatic steering system of the present invention.

lThe novel automatic navigation control system com-l prismg the subject matter of the present invention embodies a master instrument from which displacement, bank and pitch signals are available for controlling the craft in heading, as well as in position about its transverse and longitudinal axes. Repeater systems are interposed in the direction displacement channel whereby a change in heading of any desired amount may be pre-set with the system engaged by injecting an artificial displacement signal into one of the repeaters, the craft changing heading until such time as the main displacement signal catches up with and corresponds to the pre-set signal whereupon straight flight is assumed by the craft on the new heading. Furthermore, an automatic turn provision is made whereby any desired steady rate of turn may be imposed upon the craft, the proper direction displacement, bank and pitch signals for the predetermined rate of turn being automatically developed without imposing any positive load upon the master instrument normally controlling such functions.

Referring now to the single gure of the drawing, for a more detailed description of the present invention, a master instrument 10 is there shown having a magnetic field pick-up device in the form of a gyro stabilized earth inductor compass. The pick-up device comprises a triangular element 11 having laminated legs 12, 13 and 14. Each leg has wound thereon exciting windings 15, 16 and 17, each of the windings being divided into two coils, each pair of coils surrounding a related laminated leg and being connected in series opposed relation. These windings are energized from a suitable source of alternating current such, for example, as source 18. The secondary of device 11 comprises a delta connected coil 19 having three taps 20, 21 and 22 which connect by way of suitable leads 23 with a three phase wound stator 24 of an inductive coupling device 25 mounted within a master indicator shown generally by the reference character 26.

' The theory and operation of the magnetic eld pickup device or earth inductor compass is described in greater detail in copending application Serial No. 445,102, filed May 29, 1942 and now matured into Patent No. 2,710,942, 'granted June 14, 1955, to John F. Emerson. For present purposes it is only necessary to point out that each leg 12, 13 and 14 is saturated and de-saturated twice for every cycle of the exciting current flowing within primary windings 15, 16 and 17. Thus, the flux threading each leg, due to the earths magnetic field, is expelled from and re-enters each leg twice for each cycle of the exciting current. Since each pair of the coils of the primary windings 15, 16 and 17 of each leg are wound in series opposed relation, no effect is induced on secondary coil 19 by the exciting current itself. Except when the exciting current has attained a substantially maximum value, either positive or negative, the earths magnetic field is free to traverse each leg. As a result of the earths field, voltages are induced at the three taps 20, 21 and 22 of secondary coil 19 differing and dependent in value on the direction in which the pick-up element is positioned with reference to the earths magnetic field. The magnetic eld pick-up device, therefore, operates as an earth inductor compass in that for every deviation from a prescribed course, the induced voltages at the Patented Apr. 2s, 1959.

3v three taps of the secondary 19 will vary in accordance with deviation.

To provide a compass in which turning and acceleration errors are substantially eliminated so that the tendency of the compass to oscillate or overswing is prevented, element 11 is securely fastened to a rotor casing 27 of a three-degree-of-freedom gyroscope. The electrically driven rotor, not shown, of the gyroscope is pro vided with vertical spin axis, mounted within casing 27 which supports the rotor for oscillation about a first horizontal axis within a gimbal4 ring 23 by way of trunnions 29. The gimbal, in turn, is mounted for oscillation about a second horizontal axis, perpendicular to trunnions 29, within a rigid support carried by instrument 10, by means of outer` trunnions 30. A suitable erection device may be provided for maintaining the rotor spin axis normally vertical as well as a caging apparatus for caging and/or uncaging the gyro whenever desired.

lIn addition to stabilizing the earth inductor compass, the gyroscope is also provided with bank and pitch takeoifs in the form of inductive devices 31 and 32. Inductive device 31 comprises a three phase wound stator 33 having inductively coupled therewith a wound rotor 34 which is movable with trunnion 30, for example, andv inductive device 32 comprises a three phase wound stator 3S having inductively coupled therewith a wound rotor 3,6 which is movable with. trunnionsk 29. Both rotors 34 and 36 are tapped to a common conductor 37 for energization by source 18. In practice take-oifs 31 and 32 are mounted directly nn the gyroscope, take-off 31 being on the bank axis and take-offv 32 on the pitch axis. Thus, the three principal control signals are derived from a single master instrument. The advantages arising from such an arrangement are obvious, for example, the weight of the whole system is' reduce'din. that where previously at least two gyroscopes were required, i.e., a directionalV and artificial horizon gyroscope, the present system requires only one gyroscope. Moreover,` the principal controls are concentrated in a single casing whereby the device is' simple to service and any difficulties rapidlyy corrected.

For a condition of equilibrium, i.e., with the craft on a given heading and with all controls centralized, the voltages within the three windings of stator 24 of coupling device of master indicator 26 will correspond to the voltage at the three tapsl of secondary coil 19 of the pick-un device and rotors 34 and 36 of take-offs 31 and 32 will be at a given position with respect to theirrelated stator windings 33 and 35'. At the same time, a rotor winding 38 inductively coupled with stator 24 of coupling device 25 and carried byy a shaft 39, suitably journalled within master indicator'- 26, will be disposed in.

an angular position with its electrical axis normal to the resultant magnetic field ofthe three windings ofthe stator so that the voltages in the stator windings have no inductive effect on the rotor winding. As soon, however, as the craft deviates from a prescribed heading, the voltages at the three taps of secondary coil 19 will vary causing a variation in the voltages of each of the stator windings. Such change at the stator produces an angular change in the resultant of the magnetic field thereat and, since the electrical axis of the rotor winding is no longer normal to the resultant of the field at the stator, a signal is induced within rotor winding 38 which is proportional to the angle of craft deviation from its prescribed heading.

TheY electricalv signal induced Within. rotor winding 3S is: fed by means of suitable conductors 40 into a convert` tional Vacuum tube aljnplitiery 4 1. 'Lhe resulting output from amplifier 41 is fed by means of leads 42 to one phase winding 43 of a two phase induction motor 44. The second phase Winding 45 of motor 44 is continuously energized from source 18l through a conventional frequency doubler 46. Because the frequency of the in -Y duced currents within secondary 19 is twice the frequency 4 of the exciting current, a doubler 46 is included to provide like frequencies in both motor windings. A suitable phase shifting network is also embodied within the doubier so that the phases of the current within the two motor windings will be substantially apart.

Upon energization of motor phase winding 43, a rotor 47 is actuated which carries a shaft 48 having a pinion 49 thereon meshing through a reduction gear system 50 with a driven gear 51 secured to shaft 39 to drive rotor lwinding 33 to a null position, i.e., a position wherein the electrical axis of the rotor winding assumes a position normal to the new resultant of the stator field at which point the signal in rotor 38 approaches zero and phase winding 43 of motor 44 is `de-energized and the motor stops.

To provide an indication of the new heading or the amount of deviation off course, an indicating dial 52 isv carried by a shaft 53, journaled within the master indicator, the dial being adapted for angular motion relative to a fixed index 54. Angular motion is imparted to the dial from rotor shaft 39 by way of a gear 55 fastened to the `shaft and a gear 56 meshing therewith and having a hollow shaft 57 formed therewith and secured to dial shaft 53. Preferably shaft 57 is sleeved about shaft 53 and connected therewith through a compensating mechanism as shown and described in copending application Serial No. 516,488, filed December 31, 1943 and now matured into Patent No. 2,624,348, granted January 13, 1953, to P. A.` Noxon et al. By observing dial 52, the pilot will immediately know his heading. Of desired the dial indication may be reproduced at several remote stations and to this end shaft 53 carries a gear 5S for meshing with a gear 59 drivably connected with the magnet rotor 60 of an electromagnetic transmitter 61 whose stator winding connects with a similar electromagneticv receiver atthe remote station. Thisl system for reproducing motion is essentially the same as that shown and described in U.S'. Patent No. 2,342,637, issued February 29, 1944.

ln driving rotor 38 of coupling device 25 to a new` null in response to craft deviation from course, motor 44 also angularly displaces, from a normally null position, a wound rotor 62 relative to a three phase wound stator of an inductive transmitter device 63 with which the rotor is inductively coupled, the rotor winding being connected by way of a lead 64 with lead 37 for energization by source 18. By reason of the relative displacement of wound rotor 62 relative to its stator, voltages are developed at the stator which may be led directly to a rudder servo system through an amplifier to actuate the rudder. Such an arrangement, however, has the one drawback that if it is desired to set in a displacement signal independently of the earth inductor compass it could not be accomplished without disconnecting the compass from theV system.

To the end that this maybe accomplished without the necessity of disconnecting the compass from the system, novel provision is made whereby the variation in voltages developed at the stator of transmitter 63 is communicated by way of leads 65 to a three phasev wound stator of an inductive course setter device 66, normally located within a master control panel (not shown), the latter stator having inductively coupled therewith a wound rotor 67. The variation in voltages at the stator of the course setter develops an angularly movable lux vector relative to rotor 67 whereby a signal is induced in the rotor proportional to the amount Vof craft deviation from a prescribed course.

Wound rotor 67 is mounted for angular motion relative to its wound stator by means of a conventionally journalled shaft 68 which carries a roller 69 thereon for engagement with a transversely movable' disc 70 supported for rotation by a shaft 71 rwhich is fastened to a bracket 72, the free end of which is secured to a movably mounted bar 73. In addition to engaging roller'69, disc 70 also engages an integrating 'disc'74 supported by a shaft 75 driven at a constant speed by a motor 76 which is energized from source 18 by way of a lead 77 tapped to conductor 37, disc 70 normally engaging integrating disc 74 at the center thereof so that disc 70 is at rest and will not rotate at such time. The signal induced in rotor 67 is communicated to the'input of a conventional vacuum tube amplifier 78 by way of a lead 79 to a rst switch A having contacts 1 and 2, contact 1 being closed at this point,`lead 80 to a second switch B likewise having contacts 1 and 2, contact 1 being closed at this point, a resistor 81 and a lead 82. The resulting ampliiier output is fed by way of a lead 83 to energize the variable phase 84 of a two phase induction motor 85 having a rotor 86, the second phase 87 being constantly energized from source 18 by way of a lead 88. Rotor 86 is drivably coupled to move bar 73 through a gear 89 meshing with a toothed portion of the bar, the direction of movement of the bar being determined by the phase of the signal fed to the variable phase of motor 85.

Motion of bar 73 imparts a transverse movement to disc 70 from the center of rotating disc 74 whereupon disc 70 rotates causing angular motion of roller 69 and shaft 68 whereupon rotor 67 is moved toward its new null position, i.e., toward a position wherein its electrical axis lwill assume a position normal to the resultant flux vector at the stator resulting from the displacement signal generated at compass element 11. Bar 73 is also provided with a toothed portion 90 thereon for engagement with a worm 91 carried by a shaft 92 which supports a `wound rotor 93 energized from source 18 by means of a lead 94, the rotor being inductively coupled with a three phase wound stator 95.

Wound rotor 93 is normally at an electrical null with respect to wound stator 95. However, as soon as motor 85 moves bar 73 to displace rotor 67 toward its new null position, rotor 93 is displaced relative to its stator 95 whereby a signal is induced therein, the latter signal being opposite to the signal induced within rotor 67. Motion of rotor 67 toward its new null position decreases the signal therein until a point is reached where the signal of stator 95 is greater than the signal of rotor 67 whereupon the stator signal predominates and motor 85 is driven in a reverse direction moving rotor 93 back toward its original null and rotor 67 away from the new null it was attempting to attain. At this point disc 70 is moved toward the center of integrating disc 74 so that motion of rotor 67 gradually decreases. As rotor 93 approaches its null the signal from rotor 67, though diminished, predominates and again reverses operation of motor 85 until rotor 67 is finally brought to its new null position and rotor 93 assumes its original null position relative to stator 95. Anti-hunting on the part of the system is thus overcome. Associated with roller 69 may be an indicating device 96 whose indication will correspond with the indication of master instrument 26 when rotor 67 has been brought into its new null position. When the indications of master instrument 26 and instrument 96 correspond, the system is in condition to be engaged by the human pilot to automatically control craft direction of flight.

To obtain automatic control of a rudder surface 97, contacts 1 of switches A and B are opened and their contacts 2 are closed. Thereafter, any craft deviation from a prescribed course manifests itself in a signal generated by compass element 11, reproduced at the inductive transmitter device 63 and the stator of course transmitter device 66, a corresponding signal being induced 'within rotor 67 thereof which is fed by lead 79 through contact 2 of switch A to the input of a conventional vacuum tube amplifier 97a the output of which is fed by a lead 98 to the variable phase 99 of a rudder servo induction motor 100. The second phase 101 of motor i100 is constantly energizedl from source 18 by means of leads 102 and 103. Interposed between motor 100 and a rudder actuating shaft 104 is a normally disengaged clutch 105. The actuating solenoid 106 for clutch is connected through a normally open servo switch 107 by a lead 108 with a suitable source of direct current (not shown).

For automatic control, switch 107 is closed by the human pilot whereby solenoid 106 is energized to engage clutch 105 and thereby establish a driving connection between motor 100 and rudder 97. An electrical followup is provided between rudder 97 and compass 11 in the form of an inductive follow-back device having a threephase wound stator 109 inductively coupled with a wound rotor 110. Rotor 110 is energized from source 18 by way of leads 37, 77, 88 and leads 111 and 112 and is mounted on shaft 104. Actuation of shaft 104 by motor 100 produces angular displacement of wound rotor 110 from a normally null position relative to stator 109 whereby a follow-back signal is induced in the stator. This follow-back signal is fed by way of a lead 113 into amplifier 97a to be there superimposed upon the displacement signal developed at rotor 67 in the manner more fully shown in our 'copending application Serial No. 516,488, filed December 3l, 1943 and now Patent No. 2,625,348. The follow-back signal generated in stator 109 is in opposition to the direction displacement signal and increases with rudder displacement as a result of the continued operation of motor 100 until a given point is reached, at which time the signal within stator 109 is exactly equal and opposite to the direction signal to thereby wash-out the direction signal at which time motor 100 is de-energized and rudder 97 has reached an outward position in proportion to the direction signal.

With rudder 97 in its applied position and motor'100 de-energized, the craft will begin to return to its predetermined and prescribed course. The direction signal generated by the pick-up device 11 starts to diminish in value while the follow-back signal of stator 109, being at a maximum, becomes predominating and energizes motor 100 in a reverse direction to start bringing the rudder back to a neutral position. With reverse operation of motor 100, the signal in stator 109 diminishes as rotor 110 is brought back to its normally null position wherein, unless another direction signal is being generated by the pick-up device, the rudder and the direction signal generating means are in scynchronism. This condition of synchronism is desirably obtained without the provision of mechanical follow-up connections in the nature of cables, for example, between the rudder and the pickup device.

The control of the rudder by the direction displacement signal alone will invariably result in oscillations in that the craft, as it is brought back on course, tends to overswing, only to be brought back on course once more and then overswing in the original direction of departure. The net result is to cause the craft to weave about its course rather than to remain steadily thereon.

By impressing upon the direction signal, another signal that is dependent upon the crafts angular velocity or rate of turn, it is at once possible to control craft oscillation whereby dead beat steering and extreme stability under all weather conditions can be obtained. To this end, a rate of turn gyro is provided. The electrically driven rotor 114 of this rate gyro is connected by way of lead 88 with source 18 through lead 77, and the normally horizontal spin axis of the rotor is mounted by way of trunnions 115 within a gimbal ring 116 which, in turn, is mounted by way of outer trunnions 117 and 118 for oscillation about a second horizontal axis perpendicular to the spin axis. Suitable resilient members such as springs 119, for example, are connected to trunnion 117 to yieldably restrain gyro precession to a rate of turn function as is known in the art.

To generate a signal proportional to the rate of craft turn, as determined by the rate gyro. an inductive trans-- 7. mitting device is provided comprising a three' phase wound stator and a wound rotor' 121 inductively asf sociated therewith, the rotor being connected to lead 37 for energization by source 18. Rotor 121, moreover, is mounted on trunnion 118 for angular motion therewith.

The stator of inductive device 120 has a voltage generated in cach of its three windings proportional, respectively, to the angular position of cach of the windings relative to rotor 121 and is connected by a lead 122 to the input of amplifier 97a. With rotor 121 in a given null position relative to its stator, i.e., a position in which the craft has no angular velocity, no signal will be fed to the amplifier through lead 122. As soon, however, as a departure from course occurs and the craft also develops an angular velocity, rotor 121 is moved angularly relative to its stator producing induced voltages within the stator windings, the signal developed as a result of such a change being impressed upon the direction and follow-back signals within amplifier 97a.

Thus three signals, i.e., direction, rate and followback are mixed or added algebraically within the amplier to control operation of induction motor 190. During an initial craft displacement from a prescribed course, the rate signal aids the direction signal and opposes the follow-back signal so that rudder is applied more rapidly than it would be by the direction signal alone and during a return to course the rate signal (the crafts angular velocity now being in an opposite direction) opposes the direction signal but adds with the follow-back signal so that the craft is prevented from overswinging from its prescribed course once it returns thereto. This is in the nature of an anticipatorycontrol which acts to give the rudder a slight deflection in an opposite directionY when it approaches on course so that it is braked to remain on such course. lt is thus apparent. that the static rudder position by the foregoing provision is made to be algebraically proportional to the sum of the rate and direction signals.

Signals for controlling the craft about its bank and pitch axes. are derived from take-offs 31 and 32 located on gyro trunnions 29 and 30 within master instrument 1G. The stator 33 of take-off 31 is connected by leads 125l to a three phase wound stator 126 of an inductive bank trim device having a wound rotor 127 inductively coupled therewith, the rotor being connected to the input of an amplifier 128 by way of a lead 129. Rotor 127 is supported upon a shaft 130 connected to a lever 131, the free end of which is connected to a roller 133 which cooperates with a cam 134 fastened to bar 73 so that rnotion of the bar in one direction rotates the roller to angularly displace shaft 130 and rotor 127 in one direction and motion of the bar in an opposite direction rotates the roller to angularly displace shaft 130 and rotor 127 in an opposite direction.

Stator 35 of the pitch take-0E device 32, on the other hand, connects by way of leads 135 with a three phase wound stator 136, of a pitch trim device, having a wound rotor 137 inductively coupled therewith, the rotor being connected to the input of an amplier 13S by way of a lead 139. Rotor 137 is supported upon a shaft 140 connected to one end of a crank 141 whose free end is secured to a roller 142 adapted for engaging two oppositelyl inclined cams 143 and 144 so that motion of the bar in one direction rotates roller 142 along cam surface 144 to oscillate the crank about shaft as a pivot and, therefore, rotor 137 inv one direction while motion of the bar in an opposite direction rotates roller 142 alongcam surface 143 to oscillatc the crank aswell as rotor 137 in the same direction, the arrangement being such that motion of bar 73 in either direction produces angular displacement of rotor 137 in one direction only.

Three phase wound stators 126 and 136 of the bank and pitch trim devices are actually repeaters for any bank and pitch signals generated at take-offs 31 and 32 at the gyro.. A displacement of the craft in pitch and bank-rpms.A

duces relative motion of wound rotors 34 and 36 with respect to their related stators 33 and 35 whereby unbalanced voltages are developed at the stator windings which are communicated to stator windings 126 and 136. Duc to such. unbalancc in stator windings 126 and 136, the electrical axis of rotors 127 and 137 will be no longer normal to the resultant of the two elds at the stators so that signals will be induced in each of the rotors pro portional to the bank and pitch of the craft. The two signals are amplified within ampliiiers 128 and 138 and the outputs thereof are fed byv leads 145 and 146 to the` variable phases 147 and 14S, respectively, of aileron and elevator servo induction motors 149 and 150, and. the' second phase 151 of motor 149 being constantly energized from source 18 through leads 102, 103 and a lead 152', and the second phase 153 of motor 150 being constantly?` energized from sourcey 18 through leads 102, 103 and a'. lead 154.

Interposcd between motors 149 and 150 and their rcspective aileron and elevator actuating shafts 155 and 15.6 arc normally disengaged-clutches 157 and 158, each of which is provided with actuating solenoids 159, 160, the solenoids being connected through normally open switches` 161 and 162 by way of leads 163 and 164 with a suit able source of direct current (not shown).

Before switches 161 and 162 are closed to cause engagement of clutches 157 and 158 to establish a drivablo connection between motors 149 and 150 and theirV re'- spective control surfaces 165 and 166, it should be determined as to whether or nota condition of synchronism exists between the control system and the control surfaces. For example, the ailerons may be in a normally cene tralized position but a bank signal may exist within rotor 127V and at the output of amplifier 128 or there may bev no signal at the rotor but the ailerons may be displaced",v ln' either case motors 149 and 150 would be running as a result of the signals due to bank and pitch or to the dis placed surfaces so that closing of switch 161, for' ex-V ample, would develop severe jolts on the system and the craft.

Connected across the outputs of ampliers 128 andy 138 are synchronization indicators 167 and 168, which may be in the form of left-right indicators. If the craft is banked or tilted about its transverse axis even though the ailerons and elevators are centralized, the indicators will show the existence of the bank and pitch conditions; In order to eliminate the bank and pitch signals, stators 126 and 136 of the bank and pitch trim devices are mounted for angular motion relative to wound rotors 127 and 137 by way of bank and pitch trim knobs 169 and 171). These knobs may be turned to angularly displace their respective stators 126 and 136 until the resultants of the magnetic fields therein assume normal positions relative to the electrical axis of rotors 127 and 137 at which time no signals are induced in either of the rotors and indicators 167 and 168 indicate a no bank and no pitch condition.

If, on the other hand, no bank or pitch signals exist in rotors. 127 and 137 but ailerons 165 and elevators 166 are displaced from a centralized position such condition will be registered upon indicators 167 and 168, the reason being that inductive follow-back devices are provided comprising three phase wound stators 171 and 172,

each o f which is inductively associated with a relatedwound rotor 173 and 174, the rotors being tapped to lead 111. by way` of leads 175. and. 176 for energization from source 1S'. Rotor 173 is mounted for angular movement with shaft 155 relative to stator 171 and is at an electrical null with respect to its stators when ailerons 165 are in a centralized position. If the ailerons are deflected from a central position, rotor 173 is displaced to a position other than a null position at which time a signal is in ducedy in stator windings 171 and fed therefrom by a lead 177 to amplifier 128 where indicator-'167 registers such unbalance.

Rotor 174 of the elevator follow-back device, on the other hand, is mounted for angular movement with shaft 156 and is at an electrical null with respect to its stator when elevator 166 is in a centralized position. If the elevators are deflected from a central position, rotor 174 is displaced to a position other than a null position at which time a signal is induced in the stator windings 172 and fed therefrom by a lead 178 to amplifier 138 where indicator 168 registers such unbalance.

The human pilot may then operate the aileron and elevator control surfaces manually until they are centralized whereupon rotors 173 and 174 return to their null position so that the signals at stators 171 and 172 drop to zero and indicators 167 and 168 show this condition. The system is now in synchronism with the control surfaces and switches 161 and 162 may be operated to connect servo motors 149 and 150 with their respective control surfaces 165 and 166. Thereafter, any craft displacement in bank or pitch will result Ain signals induced in bank and pitch take-offs 31 and 32 which are also induced within rotors 127 and 137 and amplified within amplifiers 128 and 138 to energize variable phases 147 and 148 of motors 149 and 150. The motors, being thus energized, drive ailerons 165 and elevators 166 from their central position and simultaneously therewith rotors 173 and 174 of the follow-back devices are displaced from their electrical nulls relative to stators 171 and 172 whereby follow-back signals are generated in the stators and fed to their respective amplifiers to be there superimposed upon the bank and pitch signals. These followback signals induced within stators 171 and 172 are in opposition to the bank and pitch signals and increase with aileron and elevator displacement as a result of the continued operation of motors 149 and 150 until a given point is reached, at which time the signals induced in stators 171 and 172 are exactly equal and opposite to the bank and pitch signals at which time motors 149 and 150 are de-energized and the ailerons and elevators have reached an outward position proportional to the bank and pitch signals.

With ailerons 165 and elevators 166 in their applied positions and motors 149 and 150 de-energized, the craft Will begin to return to a centralized position. In doing so the 'bank and pitch signals at take-offs 31 and 32 diminish in value While the follow-back signals of stators 171 and 172, being at maximum, become predominating and energize motors 149 and 150 in a reverse direction to start bringing the ailerons and elevators back to their neutral positions wherein the control surfaces and the bank and pitch generating means are synchronized. As in the case of the direction `control channel, the condition of synchronism is obtained without the use of mechanical follow-up connections such as cables between the ailerons and elevators and the bank and pitch controls.

By impressing upon the bank and pitch signals, another signal which is dependent upon the crafts angular velocity or rate of turn developed during the bank and pitch or climb of the craft, it is possible to control oscillation about the bank and pitch axis which might otherwise occur. To this end, therefore, rate of turn gyros are provided, each comprising electrically driven rotors 179 and 180 connected by way of leads 181 and 182 with source 18 through lead 37, rotor 179 having a normally vertical spin axis and rotor 180 having a normally horizontal spin axis displaced 90 from the position of the spin axis of rotor 114 of the rate gyro in the direction channel, rotor 179 being mounted by way of trunnions 183 within girnbal ring 184 which, in turn, is mounted by way of outer trunnions 185, 186, for oscillation about a horizontal axis parallel with the crafts longitudinal axis and rotor 180 being mounted by way of trunnions 187 within a gimbal ring 188 which is mounted by way l0 of Iouter trunnions 189, 190, for oscillation about. vertical axis perpendicular to the crafts longitudinal axis. Springs 191 and 192 are connected to trunnions 185 and 189, respectively, to yieldably restrain gyro precession to a rate of turn function.

In order to generate signals proportional to the rate of the crafts angular velocity developed during craft bank and pitch, inductive transmitting devices are provided comprising three phase wound stators 193 and 194 having inductively associated therewith wound rotors 195 and 196, the rotors being connected for energization from source 18 by way of leads 197 and 198 tapped to lead 37. Rotors 195 and 196, moreover, are carried for angular motion relative to their stators by trunnions 186 and 190 and when the craft is centralized about its bank and pitch axes the two rotors are at an electrical null with respect to their stators. As soon as craft bank and pitch occurs an angular velocity is developed about the crafts transverse axis as well as about its longitudinal axis causing rotors 179 and 180 to precess and thereby displace the rotors relative to their stators 193 and 194 inducing in the latter signals which are led to the arnplifiers 128 and 138 by way of leads 199 and 200 to be there superimposed upon the bank and pitch signals and the related follow-back signals in the same manner and for the same purpose as described in connection with the direction displacement signal.

Novel provision is made, furthermore, for changing the direction of flight of the craft from one prescribed course to a second and predetermined course with the automatic pilot engaged and without disconnecting the compass element 11 from the system. To this end, the stator of the course setter device 66 is mounted for angular movement relative to its wound rotor 6 7 andf'to the end that such stator displacement may be accomplished, a direction trim knob 201 is provided. I

Actuation of knob 201 produces angular motion'of the course setter stator so that a signal is induced within rotor 67 thereof. The signal is fed from rotor 67 by way of lead 79 to theI input of amplifier 97a whereupon variable phase 99 of motor 100 is energized to apply rudder whereby the craft turns toward its new course an angular amount corresponding to the amount of change of course set in by knob 201. During the turn a follow-back signal and a rate signal are developed to modify the operation of motor 100 and rudder 97 in the manner hereinabove described. The craft changes course in a llat turn until such time as the signal developed from the earths magnetic field by element11 and reproduced in the stator windings of the inductive transmitter device 63 is sutiicient to move ther resultant of the magnetic field at the stator of the course setter device 66 to a position normal to the electrical axis of rotor 67 whereupon the induced signal infthe rotor diminishes to zero and the craft will have reached its new course. Thereafter, the automatic pilot maintains the craft on its new course until and unless knob 201 is again operated.

A further novel and desirable feature of the automatic pilot of the present invention is that an automatic turn may be imparted to the craft without disconnecting compass element 11 from the system. To this end, the three phase Wound stator 93 of the inductive follow-up device is mounted for angular displacement relative to its rotor 93, an automatic turn control knob 202 being provided to accomplish this purpose. By setting knob 202, a steady rate of turn of the craft may be developed with the correct bank and pitch signals automatically setin for the given rate of craft turn.

In manually displacing automatic turn knob 202, stator is angularly displaced from its normally null position relative to its rotor 93 whereupon a signal is induced in the stator and fed by way of a lead 82 to amplifier 78 and out therefrom to energize variable phase 84 of motor S whereupon the motor moves bar 73- in one direction or another, depending upon the direction of the turn set in by knob. 202, to displace disc 7i) relative to integrating disc 74r wherebyA Wound rotor 67 of the course setter device 66 is angularly displaced from its null position` relative to its stator, a signal being induced within rotor 67 and fed therefrom through. amplifier 97a to operate rudder surface 97 and thereby impart a constant rate of turn to the craft.

Simultaneously with the displacement of rotor 67 relative to its stator by bar 73, the bar, in moving likewise displaces rotors 127 and 137 of the bank and pitch trim devices` relative to their respective stators 126 and 136 whereby the correct bank and pitch signals are developed to operate the aileron and elevator surfaces the correct amount for the particular rate of turn of the craft set in byv knob 202, it beingnoted that whether the turn be toy the left or right of a given course up elevator is provided` in either case.

Follow-up motor 35, in response to the signal devel'oped at stator 95 by the turn knob, will continue to movev bar 73 until the latter has moved rotor 93 into a new null position relative to stator 95 whereupon the signal in the latter drops to zero and motor S5 becomes cie-energized. At this point disc '70 has been displaced from its normal position relative to integrating disc 74 a sufficient amount so that rotor 67 of the course setter device 66 is angularly displaced at a constant rate relative to its stator. Such operation would continue indefinitely because the displacement signal developed within rotor 67 will always be ahead of the signal communicated to the stator of the course setter device by compass element 11. Thus an automatic turn control is provided. whereby the craft may be maneuvered into an automatic turn at any desired rate without disconnecting the compass element from, the system, the turn being completed whenever knob 202 is returned manually to a normal position.

To disengage thev automatic steering system of the. present invention so that the human pilot may control the craft manually, contacts 2 of switches A and B are opened and contacts 1 thereof'closed while servo switches 107, 161' and 1962 are opened whereupon. clutches 10S, 157 and 153 disconnect the rudder, aileron and elevator surfaces from their respective servo motors 199, i@ and 150. For automatic ight, on the other hand, the human pilot opens contacts 1 of switches A and B and closes contacts 2 thereof as well as' servo switch 107 of the rudder channel. When indicators E67 and 163 indicate a condition of synchronism, switches 161 and 162 of the aileron and elevator channels are closed and thereafter, whenever the craft deviates from a prescribed course and/or a predetermined attitude the system is immediately effective to return the craft to its prescribed course and/or attitude.

Separate ampliers 97, 128 and 138 haveV been shown for the direction, bank and pitch channels, however, one amplier embodying all three channels may be used equally as well, such amplifier being shown and described in our above-mentioned Patent No. 2,625,348. Moreover, the variousinductive devices have been shown as having wound stators and wound rotors inductively coupled therewith, however, electromagnetic devices comprising wound stators having unwound magnetic rotors inductively coupled therewith. of the character described and claimed in the above referred to US. Patent No. 2,342,637 may be. used in place thereof.

There has tbus been. provided a novel all electric auto-l turn may be impressed upon the craft wherebyy upon the operation of a single knob a steady rate of turn signal is developed together with the proper bank and pitch signals required for the particular rate of turn called for.

Although but a single embodiment of the invention has been illustrated and described in detail for controlling av mobile craft about all three `of its axes, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art. For example, some of the stators of the inductive devices may be two phase wound instead of three, or `three phase wound stators may be provided but only two of the phases would be sulcient to perform the various functions described. For a definition of the limits of the present invention reference will be had primarily to the appended claims.

I claim:

1. An automatic control system for a craft having a control surface movable with respect thereto for controlling said craft about an axis thereof, comprising a servo motor for operating said surface, reference means on said craft for generating an error signal in response to a departure of said craft from a predetermined position, means interposed between said reference means and said motor for repeating said signal to energize said servomotor so that said control surface is moved in a direction to return the craft to said predetermined position, means for generating a follow-up signal in response to displacement of said surface to oppose said error signal in the energization of said servomotor whereby thev extent of movement of said surface is made to correspond to the extent of error in position and means for pre-setting a desired position change comprising a manually operable member for operating said repeating, means to provide a signal proportional to said desired position change for operating said motor.

2. An automatic control system. for a craft having a surface for maintaining the craft on a predetermined course, comprising a servo motor for displacing said surface, directional reference means comprising a magnetic eld pick-up device carried by said craft and disposed in the earths magnetic field for generating an electric signal in response to relative displacement of said pick-up device with respect to said earths magnetic field resulting from a departure of said craft from a predetermined course; further means interposed between said reference means and said motor for reproducing said electric signal therein and energizing said motor whereby said surface is moved in a direction to rest-ore said craft toy said predetermined course, means for developing an electric signal in response to said surface movement to opposey the energization of said mot-or whereby said surface is moved an amount corresponding to said displacement, and direction trim adjustment means for pre-setting a desired course change comprising a trim knob for operating said further means whereby an electric signal is developed therein independently of said reference means for operating said motor.

3. An automatic control system for a craft having a control surface movable with respect thereto for controlling said craft about an axis thereof, comprising a servo motor for operating said surface, reference means on` said craft for generating a signal in response to a departure of said craft from a predetermined position, further means interposed between said lreference. means and said motor and responsive to said signal `for developing an error signal proportional thereto for energizing said motor whereby said surface is operated in a direction to return said craft to said predetermined position, means Vfor developing a follow-up signal in lresponse yto operation of said surfaces from a normal position to oppose the. euergization of said motor by said error signal whereby said surface is operated by an amount to return said craft to said predetermined position, and position setting means comprising a manually operable member for operating said further means whereby a second signal is developed thereby independently of said reference means for energizing said motor whereby said surface is operated to course said craft to depart from said predetermined position, the departure continuing until said reference means develops a signal which balances said second signal.

4. An automatic control system for a craft having a rudder for maintaining it on a predetermined course, comprising a servo motor for operating said rudder, directional reference means comprising a magnetic field pick-up device carried by said craft and disposed in the earths magnetic eld for generating an electric signal in response to relative displacement of said pick-up device with respect to saidearths magnetic field, further means interposed between said directional reference means and said motor and responsive to said signal for developing a second signal proportional thereto, rate of turn reference means for generating a third electrical signal in response to the rate of turning of the craft, means combining said signals for energizing said motor whereby said surface is operated to return said craft to said predetermined course, and means for operating said further means whereby a predetermined fourth signal is developed therein independently of said reference means for energizing said motor to operate said rudder whereby said craft is turned to a new and predetermined course, said reference means generating an electrical signal to balance out said fourth signal when said craft has approached its new and predetermined course.

5. An automatic control system for an aircraft having a rudder for maintaining it on a predetermined course, comprising a servo motor for operating said rudder, reference means on said craft for generating a signal in response to a departure of said craft from said predetermined course, means comprising a course setter device interposed between said reference means andsaid servo motor and responsive to said signal for developing a second signal proportional thereto, means for generating a third signal in response to displacement of said rudder from a normal position, means combining said second and third signals in opposed relation to provide a resultant signal for normally actuating said motor whereby said rudder is operated in a direction and to an extent to return said craft to said predetermined course, and means for operating said course setter device to develop a fourth signal for assuming primary control of said motor to operate said rudder whereby said craft is turned to a new and predetermined course, said reference means generating a signal to balance out said "fourth signal when said craft has approached its new and predetermined course. t

6. An automatic steering system for a craft having a rudder, comprising an inductive device having a multipolar stator winding and a rotor winding in inductive relation with said stator winding, a two-phase alternating current motor connected to actuate the rotor winding of said inductive device, a source of alternating current,

`means connecting said source to energize one phase of said motor, direction responsive means comprising an induction device including a multi-polar winding connected to the multi-polar winding of said inductive device and a single phase winding energized by said source of alterhating current whereby another alternating current is generated in the multi-polar winding of said induction device, means connecting the rotor winding of said inductive device to energize the other phase of said motor whereby the latter rotates to actuate the rotor winding of said inductive device upon relative angular displacement of said direction responsive means in azimuth, an electrical transmitting device connected to said motor for :transmitting an electrical signal proportional .to the relative .angular displacement of said direction responsive means, a two-phase alternating current .servo motor for actuating the rudder of said craft, means connecting one phase of said servo motor for energization by said source of alternating current, means comprising a course-setter device and a signal amplifier connecting said signal transmitting device to energize the other phase of said servo motor whereby the latter actuates said rudder in accordance with the relative angular displacement of said direction responsive means in azimuth, and direction trim adjustment means for operating said course-setter device to develop a displacement signal to energize said other phase of said servo motor independently of said direction responsive means and without disconnecting said signal transmitting means from said course-setter device;

7. An automatic control system for a craft having a rudder for maintaining the craft on a predetermined course, comprising a servo motor for operating said rudder, directional reference means on said craf-t for providing a signal in response to a departure of said craft from a predetermined course, rate of turn reference .means for providing a second signal in response to the rate of turn of the craft, means interposed between said reference means and said motor and responsive to said signal for developing a third signal propor-tional thereto, means combining said signals for energizing said motor whereby said surface is operated to return said craft to said predetermined course, and means for operating said `further means `whereby a predetermined fourth signal isA developed therein independently of said reference means for energizing' said motor to operate said rudder whereby said craft is turned to a new and predetermined course, said directional reference means generating an electrical signal to, balance out said fourth signal when said craft has approached its new and predetermined course.A

8. An automatic control system for a craft having. a rudder for maintaining it on a predetermined course, a servo motor for operating said rudder, heading reference means on said craft for providing an error signal in response to a departure of said craft from a predetermined course, rate of turn reference means for providing a second signal in response to the rate of turning of the craft, follow-up means for providing a third signal in response to the displacement of the rudder from a normal position, further means interposed between said heading reference means and said rate of turn and follow-up means and said motor and responsive to said error signal for developing a fourth signal proportional thereto, means combining said signals for energing said motor whereby said surface is operated to return said craft to said predetermined course, and course setter means comprising a direction trim member for operating said further means to develop a third signal which over .powers said reference means control until the craft assumes a new and predetermined course.

9. In Hight control apparatus for an aircraft having an airfoil surface for controlling the attitude of the craft, which airfoil surface has a normal centered position, a motor for positioning said airfoil surface, control means of the follow-up type for producing an alternating voltage variable in magnitude and reversible in phase for controlling said motor to cause said motor to operate in a direction dependent upon the phase of said voltage and at a speed dependent upon the magnitude of said voltage, said control means including a first voltage controller automatically positioned in accordance with -the attitude of said aircraft, a second follow-up voltage controller' positioned by said motor, a third voltage control- 1er for altering the position of said surface which said control means tends to maintain, each of said controllers being adjustable in either direction from a normal position and effective to vary the magnitude and phase of said alternating voltage in accordance with the extent and direction of movement of said controller, and .means l for varying Athe extent of movement vof said motor :and hence .said airfoil ksurface resulting from `a predetermined change in the condition 'of said first controller without affecting the lposition of 'said `airfoil surface when :said airfoil surface is in its normal vcentered position.

lO. In an automatic pilot for an aircraft :having a `control surface for controlling the attitude of said craft about a-control axis, a position-'maintaining means :for-detecting movement of the craft about said control axis thereof, a servo motor means for moving the control rsurfac'e, a pick-off voltage controller, a follow-up voltage controller, a trim voltage controller, each vof said voltage controllers having a control member adjustable in either direction from ya normal position, means includingsaid ,pick-off, said follow-up and said trim voltage controllers and ,includng connections to .a source of 'alternating voltage power for producing a resultant alternating current voltage the magnitude and phase of which varies vin accordance with the algebraic sum of the directions Vand amounts of movements of said control members from their Inormal positions, phase .sensitive means responsive to ythe jphase and magnitude of said resultant alternating current -voltage for controlling the speed and direction of movement of said servo .motor means .in 'accordance with the magnitude of and the phase of said voltage with respect to the power source, means Vactuated by said positionmaintaining means for actuating the control 'member of said pick-off voltage controller to `affect the :magnitude and phase of said resultant voltage in accordance with the .extent and direction of relative deviation o f the lcraft and the position-maintaining means, imeans :responsive to `movement of the control surface for actuating Vthe control member of said follow-up voltage controller in a direction to reduce the magnitude of said resultant voltage so that the servo motor through its positioning of the control surface tends to cause said craft to be stabilized :in a predetermined attitude about said control axis, and means for manually Aactuating the 'control member of said `trim signal `controller in either one of two vdirections so as to affect the magnitude and phase of the resultant `voltage in `such a direction as to change the stabilized attitude ot `the craft in a desired direction.

1l. An automatic pilot for a craft lcomprising power means for displacing a surface of the craft, means actuated by said power means for developing a follow-up signal corresponding tothe extent and direction of displace- .ment of said surface from a normal position, an element for deriving from the earths magnetic eld an electromo- Itive force varying in accordance with the amount and direction of displacement in azimuth vof said device .relative to the earths magnetic field, a motor, a stator winding connected electrically to said element, a rotor winding inductively associated with said statorand connected electrically and mechanically to said motor, whereby the felectromotive force induced insaid rotor winding 'upon displacement of said element in azimuth operates said motor to drive said rotor winding in a direction to erase said force, course adjustment means including a pair of interconnected signal generators adapted to produce an error'signal upon loss of synchronism between the positions of said generators, the rotor of onesignal generator being positioned by said motor and the rotor of said other generator being positioned by said adjustment means, and means combining said error and follow-up signals in opposition to provide a resultant signal for operating said power means to turn said craft in a direction to erase -said signal.

1,2. Anautomatic control system for a craft comprising power means for actuating la control surface, means for developing a deviation signal whose magnitude and sense correspond to the extent and direction `of deviation of the craft from a predetermined condition, means for producinga follow-up signal whose magnitude and sense vary withthe extent and direction of displacement of the control surface from a normal position, .means comparing -said -voltages'to produce a resultant signal whose magnitude and sense correspond to the dilference between said deviation and the actuation of Vsaid control surface to correct for the deviation, means for controlling said power means by said resultant voltage to actuate said surface at a rate and in a direction determined by the magnitude and sense lof said resultant signal, and means for varying the relative portion of said follow-up signal received by Asaid comparing means whereby the extent of movement of said surface resulting from a predetermined change in Vcondition is varied without effecting the normal v`position of said surface.

13. A control system for an aircraft having a surface vfor stabilizing a craft about an axis, comprising means for developing an electrical rate signal whose magnitude 'and sense correspond to the rate and direction of turning of the craft about said axis, power means for moving said surface, means responsive to the movement of said surface .from a normal position for developing an electrical follow-up signal whose magnitude and sense correspond to the extent and direction of the movement, and Vmeans for `comparing said signals to provide a resultant signal for operating said power means to decrease said rate of tum.

14. In an automatic control system for an aircraft having a surface for stabilizing a craft about an axis, course change means for developing a signal to turn the craft to a new course, rate of turn responsive means for developing an electrical signal ycorresponding to the rate of turning of the `craftabout said axis, power means for moving said surface, means responsive to the displacement of said surface from a normal position for developing an electrical signal corresponding to the extent of displacement, and 'means for comparing said signals to provide a resultant signal to operate said power means to damp said rate of turn.

15. In an automatic control system for an aircraft having a surface for stabilizing a craft about an axis, rate of turn responsive means vfor developing an electrical signal whose magnitude andsense correspond to the rate and direction of turning of the craft about said axis, power Vmeans for moving said surface, means responsive to the movement of said surface from a normal position for developing an electric signal whose magnitude and sense correspond to the extent and direction of the movement, means for comparing said signals to provide a resultant signal to operate said power means to decrease said rate of turn, and means for adjusting the portion of follow-up signal to said comparing means whereby the extent of surface movement for a rate of turn may be adjusted.

16. An automatic control system for controlling the attitude of said craft about an axis comprising a servomotor for moving a control surface of said craft, a plurality of signal means for producing a resultant voltage for operating said servomotor, position responsive means for actuating a first of said signal means to produce a first alternating voltage whose magnitude and sense vary as a function of the extent and direction of deviation of said craft from a predetermined attitude, rate of turn means for actuating a second of said signal means to produce a second alternating voltage whose magnitude and sense vary as a a function of the rate and direction of deviation of said craft about said axis, follow-up `means for actuating a third signal means to produce a third alternating voltage whose magnitude and sense vary as a function of the extent and direction of displacement of said surface from a neutral position, and means for acthe attitude in which the craft is maintained.

17. An automatic control system for controlling the -movement of a craft about an axis comprising a servomotor for displacing a control surface of said craft, a plurality oflelectrical signal means, each signal means having a control member actuable from a null position said servomotor actuates said control surface to stabilize to produce an output signal voltage variable in sense and said craft about said axis in an attitude which is predetermagnitude in accordance with the direction and extent of mined by operation of said manually operable responsive said actuation, rst means responsive to the extent of means.

said movement of said craft for actuating the control member of a rst of said signal means, second means re- References Cited in the le of this patent sponsive to the rate of said movement of said craft for UNITED STATES PATENTS actuating the control member of a second of said signal said signal means for operating said servomotor, whereby 

